This invention relates generally to saw chain and, more particularly, to an improved center drive cutter chain for cutting wood.
Conventional saw chain generally includes a series of center drive links with depending tangs interconnected by side links. When mounted on a cutter bar, the tangs of the drive links ride in a peripheral groove centered longitudinally in the bar. The undersides of the side links run on the bar's outer parallel rails that define the groove. In one type of chain referred to herein as side link cutter chain, several of the side links include cutting elements that extend outwardly from the chain when it is mounted on the bar. Examples of such chain are disclosed in patents such as U.S. PAT. No. 2,508,784, U.S. PAT. No. 2,897,857 and U.S. PAT. No. 4,122,741. In another type of chain referred to herein as center drive cutter chain, several of the centrr drive links include outwardly extending cutting elements. An example of such chain is disclosed in U.S. PAT. No. 4,567,803.
One advantage that a center drive cutter chain has over a side link cutter chain is the side-to-side support that the depending tangs which extend into the peripheral groove provide to the cutting element. The lateral support of the tang of a cutter link lessens lateral movement of the cutter as it cuts into a workpiece.
However, a problem with both prior side link and center drive cutter chains is the vibration produced during the cutting process. As the tooth of a cutting element penetrates the wood, the cutter link is rocked rearwardly by the resistance of the wood. This rearward rocking pivotally raises the depth gauge against the wood, which limits the penetration of the cutting tooth temporarily. The cutting link is then rocked forwardly by the longitudinal tension of the chain and the cutting tooth again penetrates deeper into the wood. This repeated rocking causes the center cutter link to alternately dig into and out of the wood in a vibratory action called "porpoising." Porpoising wastes energy and reduces cutting efficiency.
The vibration problem in side link cutter chain is addressed in U.S. PAT. No. 4,122,741 to Engman et al. For each side cutter link and its oppositely disposed side link, the rear point of support on the bar rail is removed by levelling the rear underside of the link. This enables the cutting link to swivel around its forward point of support on the bar rail in response to resistance of the wood lowering the cutting tooth and its depth of penetration. Engman, however, does not disclose how the vibration in a center drive cutter chain could be reduced.